Hydrocarbon processing plants, from refineries to petrochemical plants suffer from fouling as a result of deposition of hydrocarbon byproducts deposited in heat exchangers, furnaces, water recycling loops, distillation columns, vessels, lines, overheads and other processing equipment. These byproducts include a variety of hydrocarbons that may be present in crude oil as well as the byproducts of hydrocarbon refining processes. Fouling of the interior surfaces of processing equipment occurs over a time period that may vary from months to years depending on the unit being considered.
Asphaltene deposition is a common fouling mechanism observed in refinery heat exchanger networks. Asphaltenes are naturally occurring in crude oil, wherein oil and petroleum fractions in transportation, refinery separation and other processing operations often contain asphaltenes. Asphaltenes are generally defined as a solubility class of polydisperse, high molecular weight hydrocarbons that are insoluble in non-polar solvents. They are soluble in liquids having a surface tension above 25 dynes/cm, such as pyridine, carbon disulfide, carbon tetrachloride and benzene; and insoluble in nonpolar liquids having a lower surface tension, such as low-boiling petroleum naphtha, petroleum ether, liquified petroleum gases (e.g. methane, ethane, propane), pentane, isopentane, hexane and the like. Further information regarding asphaltenes can be found in Speight, The Chemistry and Technology of Petroleum, 2nd ed., New York: Marcel Dekker, Inc., pp. 96-97, and 404-451 which is hereby incorporated-by reference herein.
Asphaltene particles are believed to exist in the form of a colloidal dispersion stabilized by other components of crude oil. These naturally occurring dispersions can be destabilized by a variety of mechanical, thermal, and chemical conditions involved in oil production and processing. Blending of incompatible crude oils may also result in destabilization of asphaltenes. This destabilization may result in asphaltene aggregation, precipitation, and eventual deposition of a tarry residue on the processing equipment. Other high-molecular weight hydrocarbon foulants include heavy oil, tars, polynuclear aromatic hydrocarbons, and coke; polymers formed from polymerization of vinylic byproducts of petroleum processing such as styrene, butadiene, cyclopentadiene, and the like; aliphatic and aromatic hydrocarbons having a density less than that of water, commonly referred to as light oil; oxidized hydrocarbons; and thermal decomposition products resulting from the degradation of larger molecules, such as one of the foulants listed above, either alone or combined with one or more other compounds present in a petroleum mixture. All these foulants are of concern to the operators of hydrocarbon processing plants.
Asphaltenes and related foulants are an acknowledged issue in petroleum processing and are known to cause problems related to fouling in various types of equipment where these compounds contact interior surfaces thereof. Unless dissolved and/or effectively dispersed, asphaltenes and other foulants can accumulate and precipitate upon any one or more surfaces contacted within processing equipment or storage containers, causing fouling. Fouling causes a plethora of problems in a range of petroleum processing operations.
In one illustrative example of the foregoing problems, dilution steam systems employed in pyrolysis processes such as ethylene production processes often undergo fouling due to polynuclear aromatics (PNAs) and related foulants. If unchecked, these foulants can deposit on interior surfaces of the dilution steam system, lowering flow within the system or even plugging flow lines and paths; interfering with internal measurement equipment such as thermocouples etc. used to monitor the process flow; and lowering the efficiency in the processing pathway. Regular cleanings to remove foulants from interior surfaces of dilution steam systems is a major source of pyrolysis plant downtime.
Another illustrative example is fouling during hydrotreating. The hydrotreating is a catalyzed hydrogenation process that leads to the conversion of nitrogen and sulfur containing contaminants to hydrogen sulfide and ammonia. It is also used to convert aromatics and olefins into saturates. Processing of reactive hydrocarbon streams during hydrotreating leads to the formation of synthetic foulants under various conditions of thermal and oxidative polymerization of olefinic compounds. The foulants formed, or synthesized, during such processes adhere to the processing equipment surface, such as preheat exchangers, resulting in reduction of the unit throughput and pressure drop across heat exchanger tubes.
The foulants that accumulate and precipitate onto such petroleum processing surfaces as demonstrated above—as well as many other examples—are notoriously difficult to remove. Consequently, there is an ongoing need for new methods and compositions to effectively disperse asphaltene and related natural and synthetic foulants in petroleum processing systems in order to prevent interruptions for cleaning, protect downstream equipment, and increase the overall efficiency of petroleum processing.
Comer et al., U.S. Pat. No. 5,214,224 discloses olefin-maleic anhydride copolymers useful for antifouling of hydrocarbon streams. However, these anhydride functional polymers are reactive toward hydrolytic conditions, undergoing ring-opening addition of water to the anhydride functionalities. The hydrolyzed anhydride polymer does not have anti-fouling properties and being insoluble in hydrocarbon can potentially be a foulant itself. Thus, the anhydride-functional polymers are unsuitable for use in processing streams contaminated with water. Further, hydrolysis of anhydride functionalities may take place slowly over time even in a substantially dry petroleum product where water is an impurity of the petroleum product. Additionally, the olefin-maleic anhydride copolymers tend to either precipitate from petroleum products or form viscous, even solidified blends therewith at low temperatures, such as temperatures encountered in the field during winter petroleum processing operations.
There is a need to provide stable dispersions of natural and/or synthetic foulants in petroleum process streams during one or more petroleum processing operations. There is a further need to form stable dispersions of natural and/or synthetic foulants in petroleum products in high temperature environments existing during refining processes. There is a further need to provide concentrates of antifouling compositions that are stable dispersions and are pumpable or pourable to temperatures of about 0° C. to −40° C.